The leading cause of lower back pain arises from rupture or degeneration of lumbar intervertebral discs. Pain in the lower extremities is caused by the compression of spinal nerve roots by a bulging disc, while lower back pain is caused by collapse of the disc and by the adverse effects of articulation weight through a damaged, unstable vertebral joint. One proposed method of managing these problems is to remove the problematic disc and replace it with a prosthetic disc that allows for the natural motion between the adjacent vertebrae (“a motion disc”).
U.S. Pat. No. 6,368,350 (“Erickson”) discloses a three-piece motion disc providing two articulation surfaces. The disc comprises a first piece having a curved surface, a second piece having a flat surface, and an intermediate piece having a corresponding curved articulation surface and a corresponding flat articulation surface. Lastly, Erickson teaches that a variety of materials can be selected as materials of construction for the components of its device, including metals, polymers, and ceramics, and specifically teaches preferred combinations including metal-metal or metal-plastic combinations.
Erickson does not teach providing a shock-absorbing component in addition to the articulating component between the prosthetic endplates.
U.S. Pat. No. 5,676,701 (“Yuan”) discloses, in one embodiment, a motion disc having a single articulation surface. This device includes a first component whose inner surface comprises a concave inner portion having a 360° circumference and a convex peripheral portion, and an opposing second component whose inner surface comprises a conforming convex inner portion and a convex peripheral portion. The convex/concave contours of the opposing inner portions forms a ball-and-socket design that allows unrestricted pivotal motion of the device, while the opposing convex peripheral contours allow flexion/extension bending motion in the range of about 20–30°.
However, Yuan does not teach providing a shock-absorbing component in addition to the articulating component between the prosthetic endplates.
U.S. Pat. No. 5,507,816 (“Bullivant”) discloses a three-piece motion disc providing two articulation interfaces and comprises an upper piece having a flat lower surface, a middle spacer having a flat upper surface and a convex lower surface, and a lower piece having a concave upper surface. The articulating convex and concave surfaces form an articulating interface that allows pivotal motion, while the flat surfaces form a translation interface that allows translational motion.
Bullivant does not teach providing a shock-absorbing component in addition to the articulating component between the prosthetic endplates.
U.S. Pat. No. 4,759,766(“Buttner-Janz”) discloses a motion device comprising three components: an inferior endplate, a superior endplate, and a core having two articulation interfaces. Both the inferior and superior endplates are metal and have raised bosses with concave spherical surfaces in the center. The core is plastic and has convex surfaces on both the top and bottom which are surrounded by raised rims.
Buttner-Janz does not teach providing a shock-absorbing component in addition to the articulating component between the prosthetic endplates.
U.S. Pat. No. 5,314,477 (“Marnay”) discloses a device having a single articulation interface and comprises three components: an inferior endplate, a superior endplate, and a plastic insert. The inferior endplate functions as a baseplate and has a sidewall forming an open ended channel for reception of the insert. The inner surface of the inferior endplate provides only stationary support for the insert and does not have a motion surface. Since the plastic insert is designed to be locked securely into place within the inferior endplate, the inferior surface of the insert is not a motion surface. The superior surface of the insert includes articulation surface for articulation with the superior endplate. The superior endplate has an inferior articulation surface that articulates with the superior motion surface of the plastic insert, and a superior surface designed for attachment to a vertebral endplate.
Marnay does not teach providing a shock-absorbing component in addition to the articulating component between the prosthetic endplates.
French Published Patent Application No. 2,730,159 (“Germain”) discloses a motion disc in which the core member has one convex and concave surface. Germain further teaches that the radius of the upper curved surface (3a) of the core member is less than the radius of the lower curved surface (3b) of the core member.
Germain does not teach providing a shock-absorbing component in addition to the articulating component between the prosthetic endplates.
U.S. Pat. No. 5,824,094 (“Serhan”) discloses a cushion-type motion disc wherein a rubber core is sandwiched between two metal prosthetic endplates. The rubber core provides a shock-absorbing effect and so mimics the natural response to axial load. However, the rubber core was found to experience high shear stresses in use.
In sum, the prior art does not disclose a motion device having two articulation interfaces that provides for both articulation and shock-absorption.